As the public attention to the harm to the natural environment increases energy consumption with a low efficiency is more and more criticized. Especially the fossil generation of energy is in the focus of the critic since the carbon dioxide concentration in the atmosphere is increasing and is suspected to cause a green house effect. Therefore it is planed to penalize the production of carbon dioxide with so called CO2-certificates. This political development increases the economic interest in technology, which enables energy production with low emission. Even stricter handled is the emissions of nitro oxides, which are suspected to cause even more serious damage to the natural environment.
In this context the efficiency of cogeneration, in particular the efficiency of an arrangement with a steam turbine and a condenser becomes extremely interesting as this arrangement is one of the most powerful devices to generate energy out of heat, which often is a waste product of a higher ranking process. A very important issue is to keep the cogeneration very flexible with regard to the thermodynamic boundary conditions to reach always the highest efficiency possible.
One example for an environmental-friendly cogeneration is the energy and heat generation using oxyfuel. Purified oxygen is mixed with a fuel, in particular with methane and burned under a pressure of proximately 30 bar and in an atmosphere of exhaust gas, which was fed back to obtain a high concentration of carbon dioxide, which afterwards is purified and liquefied. This very special process has several constraints and the waste heat has therefore very specific thermodynamic parameters, which make it difficult to set up a highly efficient cogeneration with a steam turbine.
In the U.S. Pat. No. 6,047,549 B1 a power plant facility is described combining a gas turbine with a waste heat boiler in flow connection with a condensing steam turbine. In this arrangement the gas turbine, the waste heat boiler and the steam turbine are finally tuned to each other and therefore reach efficiencies of up to 58%. The term “waste” can not really be applied to the heat of the exhaust gas of the gas turbine since the gas turbine was designed from the beginning on to supply this heat to the boiler, which is generating steam for the steam turbine. So far, no concept is known to use waste heat not having proper conditions to operate a steam turbine with a high efficiency.